1. Field of the Invention
The present invention relates to a vehicle detection system for detecting a passage of a vehicle in a non-contact manner, and more particularly to a vehicle detection system capable of discriminately detecting between predetermined specific vehicles and other vehicles and being usable at a parking area or the like.
2. Description of the Related Art
Loop coils buried in the ground have been generally used as a vehicle detection system for managing vehicles incoming and outgoing a parking area. A detection principle of this vehicle detection system is as follows. When a vehicle comes over a loop coil, a parameter of the loop coil changes and this change is detected. For example, when the inductance of a loop coil changes, this inductance change is detected to detect that a vehicle is over the loop coil, and a detection signal is generated.
A conventional vehicle detection system of such a type is shown in FIG. 9. In a conventional vehicle detection system 100, a loop coil 1 buried under an inlet road of a parking area forms a resonance circuit with a capacitor 102 of a self-oscillator 101 which oscillates at the resonance frequency of the resonance circuit. An oscillation output of the self-oscillator 101 is supplied to a frequency discriminator 103 which generates a d.c. voltage corresponding to the oscillation frequency of the self-oscillator 101. A d.c. voltage output from the frequency discriminator 103 is supplied to an A/D converter 104 to convert it into a digital signal. This digital signal is supplied to a controller 105 which compares it with a predetermined threshold value to detect the vehicle.
When a vehicle A comes over the loop coil 1, the inductance of the loop coil 1 lowers because of an eddy current loss by a vehicle body and the oscillation frequency of the self-oscillator 101 shifts to a higher frequency. Therefore, an output of the A/D converter 104 exceeds the threshold value. The controller judges that the vehicle A is over the loop coil 1, and generates a vehicle detection signal. In response to this vehicle detection signal, a ticket vendor 2 and a car gate driver circuit 3 are operated to issue a parking ticket, and when the parking ticket is picked up by the driver, a car gate 4 is opened. In this manner, vehicles incoming and outgoing the parking area are managed. The frequency discriminator 103 is realized by a ratio detector or the like. It can also be realized by a frequency counter. In this case, the A/D converter 104 can be omitted and the count of the frequency counter is directly supplied to the controller 105 to process it.
Charged parking areas include a time charging parking area which charges in accordance with the parked time and a monthly contract charging parking area which contracts on a month unit basis. Most of large time charging parking areas also provide monthly contract charging. Almost all such combined parking areas have a space in the parking area for allowing vehicles of persons in charge of the parking area to be parked.
Such combined parking areas provide services of giving a card to each driver of a specific vehicle such as a contracted vehicle and a vehicle associated with the parking area, and allowing the driver to freely come in and go out of the parking area. Although such a card is used generally by inserting it into a ticket vendor or a fare adjuster, there is a card of a different type whose contents can be read while the driver holds it up in the vehicle. A parking area in/out management system which allows both types of cards has a non-contact card reader. A non-contact card is called a transponder of a non-contact discrimination system which is formed in a card shape.
A vehicle management system of a parking area using both a vehicle detection system and a non-contact card reader is configured as shown in FIG. 10. FIG. 10 shows the parking area incoming side. As shown in FIG. 10, this system is constituted of a non-contact card reader 107 with a card antenna 106, a vehicle detection system 100A with a loop coil 1A, a ticket vendor 2, a car gate driver 3, and another vehicle detection system 100B with a loop coil 1B, all being connected to a controller 105A and disposed in this order from the upstream side of the inlet road of the parking area. The vehicle detection systems 100A and 100B have the structure same as the vehicle detection system 100 shown in FIG. 9. When the controller 105A detects that a vehicle comes over the loop coil 1A, it operates the ticket vendor 2 and car gate driver 3. After the ticket is issued, a car gate 4 is opened. When the controller 105A detects that the vehicle comes over the loop coil 1B, it operates the car gate driver 3 to close the car gate 4. The parking area outlet side is structured in a similar manner except that the ticket vendor is replaced by a fare adjuster.
However, although it is convenient if such a conventional non-contact card reader is provided in combination with an insertion type card reader, the conventional system is associated with some problems. One problem is that a driver is required to carry a card and hold it up when the vehicle comes in and goes out a parking area. If the driver does not hold the card up inadvertently and the vehicle comes over the loop coil, then the ticket vendor issues a parking ticket. Even in such a case, the parking area is required to be managed so that if the driver holds the card up thereafter toward the card reader, the vehicle is allowed to come in the parking area, and the parking ticked once issued becomes wasteful. Another problem is that an illegal parking cannot be inhibited if a card is transferred to a third party from its owner. Another problem is that if a non-contact vehicle discriminator system which discriminates vehicles from vehicle numbers by using image recognition techniques, is used, the camera installation position is limited and the system is expensive.
Some non-contact card readers utilize radio waves, whereas others utilize magnetic fields.
In the former case, a read performance is deteriorated by rains and snows. In such a case, an antenna cannot be buried in the ground, but it is mounted above the ground. There arises therefore a problem that dust-proof and robbery-proof of an antenna is necessary increasing the cost. If a non-contact card reader utilizes microwaves, it is necessary to mount the antenna at the position where a stable read operation is possible in terms of radio wave transmission characteristics, thus posing a problem of a position limitation. Further, in this case, a transponder cannot be mounted under the vehicle body, but it is mounted on the front side of the vehicle body thus degrading the decorative performance of the vehicle body. Also the non-contact card reader utilizing microwaves is associated with some problems that the transponder requires a battery as its power source and is expensive and that the reader is required to receive the model acceptance as a radio wave equipment.
In the latter case, the non-contact card reader utilizes magnetic coupling or magnetic induction. Therefore, a read performance is not affected by rains and snows, an antenna can be buried in the ground, dust-proof and robbery-proof are not necessary, and a transponder can be mounted conveniently under the vehicle body. The distance between the transponder mounted under the vehicle body and the antenna buried under the ground is approximately a distance between the ground surface and the bottom of the vehicle body, so that a stable and less-variation read performance is possible, and the decorative performance of the vehicle body is not damaged. Further with magnetic coupling or magnetic induction, the transponder is not necessary to use a battery, and the reader is not required to receive the model acceptance as a radio wave equipment. However, in the latter case, the frequency range used by the card reader is several tens kHz to several hundreds kHz. The frequency range used by the vehicle detection system is generally several tens kHz to several hundreds kHz near to the above-described frequency range because the inductance of the loop coil is about several tens xcexcH to several hundreds xcexcH. Therefore, there arises an interference problem that the non-contact card reader using magnetic coupling or magnetic induction and the vehicle detection system cannot be used at the same time.
It is an object of the present invention to provide a vehicle detection system capable of being applied to vehicle management not only for a time charging parking area which charges in accordance with the parked time but also for a combined charging parking area which incorporates both the time charging and monthly contract charging, by providing a non-contact vehicle discriminator system utilizing magnetic coupling or magnetic induction.
According to the first aspect of the vehicle detection system of the invention, a vehicle detection system for detecting an arrival of a vehicle in non-contact with the predetermined vehicle comprising; a first inductive element for functioning as transmitting and receiving means a first vehicle detecting circuit connected to the first inductive element, and a transponder mounted on a predetermined vehicle, storing information which identifies the predetermine vehicle, periodically activated by a magnetic field which the first inductive element generates, periodically transmitting the stored information to the first vehicle detecting circuit via the first inductive element, wherein the first vehicle detecting circuit periodically stimulates the first inductive element to generate the magnetic field, the transponder activated during a stimulating period for the first inductive element transmits the stored information to the first vehicle detecting circuit via the first inductive element during a non-stimulating period for the first inductive element when the transponder mounted vehicle has enter into a specified area arranged the first induct element, and the first vehicle detecting circuit detects the arrival of the predetermined vehicle by using the received information from the transponder.
According to the second aspect of the vehicle detection system of the invention, a vehicle detection system comprises: an inductive element mounted at a predetermined position; a transponder selectively mounted on a vehicle, the transponder storing information indicating the vehicle mounted with the transponder is a predetermined vehicle; and a first vehicle detection circuit for magnetically coupling the inductive element when the vehicle mounted with the transponder enters a predetermined area in front of the inductive element, and receiving the information stored in the transponder to detect that the predetermined vehicle enters the predetermined area.
In the vehicle detection system of this invention, when a vehicle mounted with a transponder enters a predetermined area in front of the inductive element, the transponder and inductive element are magnetically coupled with each other, and the information stored in the transponder is read by the first vehicle detection circuit. In accordance with the read information, it is possible to detect that a predetermined vehicle enters the predetermined area in front of the inductive element.
Since magnetic coupling is used, the transponder can be made compact and can be mounted under the vehicle body so that the decorative performance of the vehicle body is not damaged. Further with magnetic coupling, it is not necessary to receive the model acceptance as a radio wave equipment, and the transponder can be made inexpensive. As compared with a non-contact card reader using microwaves, the transponder is not necessary to use a battery, and is more inexpensive.
Furthermore, since magmatic coupling is utilized, influence by rains and snows is not present. Since the inductive element can be buried in the ground, dust-proof and robbery-proof are not necessary. The transponder can be mounted conveniently under the vehicle body. The distance between the transponder mounted under the vehicle body and the inductive element buried in the ground is approximately a distance between the ground surface and the bottom of the vehicle body, so that a stable and less-variation read performance is possible, and the decorative performance of the vehicle body is not damaged.
In the vehicle detection system, the first vehicle detection circuit may time divisional supply the transponder with an operation energy through magnetic coupling with the transponder, or may perform a supply of an operation energy to the transponder and a reception of information from the transponder, and the inductive element is used for both the supply of the operation energy and the reception of the information. In this case, the transponder is not necessary to use a battery as a power source, and the inductive element can be effectively used in common.
The vehicle detection system may further comprises a second vehicle detection circuit magnetically coupling the inductive element for detecting a presence of a vehicle over the inductive element in accordance a change in an electric parameter of the inductive element to be caused by the vehicle on the inductive element. If the second vehicle detection circuit is provided, it is possible to detect that not only a vehicle mounted with a transponder but also a vehicle without a transponder comes over the inductive element. It is therefore convenient that this vehicle detection system can be used by a combined parking area incorporating both time charging and monthly contract charging.
The second vehicle detection circuit may detect a presence of a vehicle in accordance with a phase of an output signal obtained through magnetic coupling with the inductive element, may detect a change in the electric parameter of the inductive element from a voltage charged in a capacitor and detect a presence of a vehicle in accordance with a phase of the charged voltage, or may detect a presence of a vehicle in accordance with a level of output voltage obtained through magnetic coupling with the inductive element. As above, various detection methods can be selectively used and an application field of this system can be broadened.